The team led by Prof. Ting Guo has patented a system in which a therapeutic molecule—the cancer drug—is connected via a DNA linker to a metal nanoparticle. This might be based on gold or silver, for instance, and can be coated in something flagging it for delivery to the tumor, like an antibody. The nanoparticle itself functions as the carrier and can shuttle many molecules of the drug to the desired destination. The whole ensemble is inactive until the x-ray trigger is applied. This cleaves the linker, releasing the active drug molecules directly into the tumor, where they can go about destroying the cancer cells they were designed to kill.
Image: Synthesized nanoparticle drug carriers, imaged using transmission electron microscopy (TEM)(Source: http://www.google.com/patents/US20140273215)